SummaryThe 3 - (1’- phenylpropyl) 4 - hydroxycoumarine (marcoumar) is an efficacious anticoagulant; because of its long and definite action, it is particularly maniable.Its action is characterized by a drop of Koller factor VII and prothrombine and can be controlled by Quick method or more easily by the Marbet and Winderstein method.During the treatment of acute thrombosis, simultaneous heparin administration is necessary until the full action of the drug is reached.36 patients have been submitted to the action of this drug. All the cases of spontaneous or postoperative venous thrombosis responded very well. No case of pulmonary emboli has been observed during the evolutionary course of venous thrombosis, and no recidive in patients having presented previously pulmonary emboli.Hemorragic accidents consisted in microscopic hematuria (8 times out of 36) and deep hematoma (one out of 36).Synthetic vit. K1emulsion is an efficacious antidote bringing back quickly the prothrombine time to harmless levels.